Various processes are known for upgrading hydrocarbon streams, such as natural gas condensates and crude oil fractions with boiling point characteristics similar to natural gas condensate, by fractionation and conversion, including reforming, of certain fractions thereof. This is illustrated by the following patents, which have been cited in a report based on a search directed to the present invention:
U.S. Pat. Nos. 3,281,351--Gilliland et al.
3,388,055--Craig et al.
3,406,217--Davison et al.
3,409,540--Gould et al.
3,732,085--Carr et al.
3,761,392--Pollock;
4,000,206--Drehman;
4,162,214--Maslyansky et al.
4,222,854--Vorhis, Jr., et al.
In the process disclosed in the Vorhis et al patent, a naphtha feedstock with a boiling point range of 100.degree.-550.degree. F., is fractionated and the mid-cut (boiling point 220.degree.-300.degree. F.) is reformed. Separately, the lower and upper fractions are recombined and reformed, all of the reforming being directed to produce gasoline components.
In the Carr et al process, crude oil is fractionated and its heavier components hydrocracked to produce naphtha, which is in turn reformed along with a middle fraction of the crude to form synthetic natural gas. Benzene, however, is apparently not a significant product in this process.
Maslyansky et al enhances between production from reformate by hydrocracking a high boiling fraction of the reformate and separating aromatic products from the hydrocracked product while recycling the remainder for further hydrocracking, so as to upgrade substantially all of the reformate to aromatic products. Some gaseous by-products, with ethane predominating in the examples, is also produced in the hydrocracking process; toluene is recycled so that the primary reaction is one of dealkylation of higher aromatics to benzene; the process conditions, hydrogen atmosphere, elevated temperature, a pressure of 10-60 atmospheres, and a catalyst consisting of mordenite and a hydrogenating agent, are apparently designed to maximize aromatic yield, not gasified products.
Unlike the other references cited above, the Drehman patent indicates that the feedstock in the process of that patent may be a natural gas liquid. This feedstock is said to be a C.sub.6 hydrocarbon stream which is converted to benzene, a cyclohexane, and a motor fuel blending stock by fractionation, hydrogenation, and isomerization. The benzene and fuel gas result from fractionation of a reformate produced from a feedstock consisting primarily of normal hexane, in turn produced as a middle cut from a succession of three fractionators. Substantially all other fractions are hydrogenated, isomerized, and fractionated to produce motor fuel and cyclohexane, and none is gasified.
The remaining patents cited above are of interest only for their showing of separate treatment of fractionated crude oil or gasoline stocks, some fractions of which are separately hydrocracked or, as in the Pollock and Gould et al patents, reformed.
None of the known published references suggest a process, as in the present invention, involving the integrated conversion to benzene and synthetic natural gas, of natural gas condensate.
Another process is known, however, though not known to be disclosed in any published reference, in which natural gas condensate is converted to benzene and synthetic natural gas streams by reforming essentially the entire natural gas condensate feedstock, then separating benzene therefrom and gasifying the remainder.
Notwithstanding this prior art, there remains a need for further upgrading natural gas condensate and more particularly a need for a process to enhance the product value yield of the natural gas condensate conversion.
It is therefore a general object of the present invention to provide a process for increasing the proportion of benzene in the benzene, synthetic natural gas product mix of a gas condensate conversion process.